docs: Port the man pages from DocBook to reStructuredText

So they are consistent with the way we’re building man pages in other
projects, and because some people are allergic to XML.

This changes the build-time dependencies from `xsltproc` to `rst2man`,
and also takes the opportunity to change the `-Dman` Meson option from a
boolean to a feature (so you should use `-Dman-pages={enabled,disabled}`
now, rather than `-Dman={true,false}`).

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3037

docs/reference/gobject/gobject-query.rst

@@ -0,0 +1,74 @@
+.. _gobject-query(1):
+.. meta::
+   :copyright: Copyright 2003 Matthias Clasen
+   :copyright: Copyright 2012 Red Hat, Inc.
+   :license: LGPL-2.1-or-later
+..
+   This has to be duplicated from above to make it machine-readable by `reuse`:
+   SPDX-FileCopyrightText: 2003 Matthias Clasen
+   SPDX-FileCopyrightText: 2012 Red Hat, Inc.
+   SPDX-License-Identifier: LGPL-2.1-or-later
+
+=============
+gobject-query
+=============
+
+-----------------------
+display a tree of types
+-----------------------
+
+SYNOPSIS
+--------
+
+|  **gobject-query** froots [*OPTION*…]
+|  **gobject-query** tree [*OPTION*…]
+
+DESCRIPTION
+-----------
+
+``gobject-query`` is a small utility that draws a tree of types.
+
+It takes a mandatory argument that specifies whether it should iterate over the
+fundamental types or print a type tree.
+
+COMMANDS
+--------
+
+``froots``
+
+  Iterate over fundamental roots.
+
+``tree``
+
+  Print type tree.
+
+OPTIONS
+-------
+
+``-r <TYPE>``
+
+  Specify the root type.
+
+``-n``
+
+  Don’t descend type tree.
+
+``-b <STRING>``
+
+  Specify indent string.
+
+``-i <STRING>``
+
+  Specify incremental indent string.
+
+``-s <NUMBER>``
+
+  Specify line spacing.
+
+``-h``, ``--help``
+
+  Print brief help and exit.
+
+``-v``, ``--version``
+
+  Print version and exit.